This invention relates to pistons for use in engines having direct-injection fuel systems.
Spark-ignition, direct-injection combustion systems for internal combustion engines have been proposed to improve fuel economy when compared with more typical port fuel-injected combustion systems. The spark-ignition, direct-injection engine is provided with a high pressure fuel injection system that sprays fuel directly into the engine combustion chamber which is formed, at least partially, in the piston. The fuel is directed or transported to a specific region within the combustion chamber. This creates a stratified charge in the combustion chamber resulting in fuel economy benefits since the throttling requirements are less restrictive and the fuel combustion characteristics are improved. It has become the practice of engine designers to incorporate design features in the piston toward this end.
U.S. Pat. No. 5,553,588 issued Sep. 10, 1996, for example, discloses a combustion chamber design with improved fuel distribution in mind. This prior art describes a combustion chamber that is partially formed in the piston. The combustion chamber has a plurality of fuel regions defined by walls including two arcuate-shaped regions interconnected by a linear region. These regions cooperate to accommodate swirling of the fuel entering the combustion chamber. The ignition source, a spark plug, is positioned with the electrodes protruding into the combustion chamber near the linear region and the fuel is injected at one of the arcuate regions.
U.S. Pat. No. 6,035,823, issued Mar. 14, 2000, describes a piston, injector and igniter combination wherein the piston has a circumferential wall having a predetermined radius and wherein the center of the circumferential wall is located a predetermined distance from the injector. The circumferential wall has an arc-shaped cross section that redirects the fuel toward the igniter. The piston configuration of this patent requires that the injector have a flat sector-shaped spray pattern.
It is an object of the present invention to provide an improved combustion chamber having a portion thereof defined in the piston head.
In one aspect of the present invention, the combustion chamber is formed between a cylinder head and a piston with a piston bowl being formed therein. In another aspect of the present invention, the piston bowl has a floor and a transporting surface. In yet another aspect of the present invention, the combustion chamber has exhaust squish surfaces and intake squish surfaces formed between the piston external of the bowl and a combustion chamber surface on the cylinder head. In still another aspect of the present invention, the piston bowl volume is in the range of 50% to 70% of the total volume of the combustion chamber at piston top dead center.
In yet still another aspect of the present invention, the bowl depth and the location of the transporting surface have dimensional ranges that are essential to the present invention. In a further aspect of the present invention, the exhaust squish heights are in a range of 2-6 mm. In yet a further aspect of the present invention, the upper edge of the transporting surface is located in the range of 6-10 mm from the centerline of the ignition source and has an included negative draft angle in the range of 0 to xe2x88x9220 degrees. In still a further aspect of the present invention, the bed of the bowl and a flat portion or the upper edge of the transporting surface are connected by an arcuate surface that is tangential to both.